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The policy would include sites that distribute fake news. It could give sites a bigger incentive to get things right or risk losing a valuable source of revenue.

Facebook followed with an announcement that fake news sites are also banned from using its ads.

"In accordance with the Audience Network Policy, we do not integrate or display ads in apps or sites containing content that is illegal, misleading or deceptive, which includes fake news," Facebook said in a statement to Forbes. "While implied, we have updated the policy to explicitly clarify that this applies to fake news. Our team will continue to closely vet all prospective publishers and monitor existing ones to ensure compliance."

Days earlier, Facebook CEO Mark Zuckerberg said the company was taking steps to keep fake news stories out of users' News Feeds.

The moves come after criticism that the spread of false stories and misinformation could have influenced the outcome of the U.S. presidential election -- something that Zuckerberg said is highly unlikely.